Facile preparation of aqueous fullerene C60 nanodispersions

Abstract

Aqueous solutions of the fullerene C60 (nC60) were prepared by simple mixing of the solution of C60 in N-methylpyrrolidone (MP) with deionized water or an aqueous solution of a low-molecular-weight natural substance (L-amino acids, monosaccharides, peptides, or glycerol) used as stabilizing agents (SAs) followed by exhaustive dialysis against distilled water. During dialysis, all low-molecular-weight compounds are removed through the pores and the fullerene clusters remain in the solution. The efficiency of conversion of C60 from the crystalline state to the solution approaches the quantitative value, and solutions with a C60 concentration of up to 250 mg/L can be obtained; moreover, these solutions are stable for at least 10–12 months. The formation of insoluble aggregates has been observed when basic and acidic organic compounds were used as SA. The UV-VIS spectra of solutions have a profile characteristic of nC60 solutions obtained by other well-known procedures (maxima at 220, 265, 340, and 450 nm). Mass spectra of aqueous solutions and FTIR spectra of dried nC60 samples were indicative of the possible partial hydroxylation of the fullerene. A measurement of the sizes and ξ potential of the C60 particles in solutions by the dynamic light scattering method showed that their average diameter is about 100 nm and the charge is −30 mV, whereas the electron microscopy data demonstrated that the particles have a typical size of approximately 20 nm and contain both crystalline and amorphous phases. The proposed method is promising for the preparation of solutions of endofullerenes and, probably, higher fullerenes.